Spray nozzles are generally used to atomize liquids. One conventional type of nozzle, generally characterized as an "airless" spray nozzle, is used in conjunction with airless spray equipment to force the paint stream through a small orifice under a relatively high pressure, as for example, a pressure on the order of about 300 to 3,000 psi. As the paint is propelled through the small orifice, it is broken up or atomized into very fine droplets. The paint spray dispensed from the orifice then moves at a relatively low velocity toward the article to be painted. Typically, the paint spraying operation is carried out with the atomized paint particles charged to a relatively high electrostatic potential and with the workpiece or article to be coated at, or close to, ground potential. The particles are then additionally urged toward the workpiece by the forces of the electrostatic field. This airless type of spraying has the recognized advantage of providing a very high deposition efficiency, i.e., a large portion of the paint spray emitted from the gun is effectively deposited on the article to be coated. Airless spray nozzles are also used for non-electrostatic applications.
A characteristic of many paints is that they contain a substantial portion of abrasive materials. In the course of passage through the nozzle orifice at a relatively high pressure, as in the airless spray systems, paints tend to wear or abrade away the nozzle orifice. Consequently, the nozzle orifice is usually formed in a nozzle tip made from a material having a high resistance to abrasion. Such a tip is commonly manufactured from a very hard material, as for example, tungsten carbide. Even when manufactured from a very hard material, the nozzle tips are subject to wear and must be regularly replaced. Being a replaceable item, the nozzles are therefore manufactured as inexpensively as possible.
One common expedient for minimizing the cost of the nozzle is to manufacture the nozzle in two pieces, one a small nozzle tip of very hard, abrasive resistant, material and the other a more easily machined, less expensive but less abrasive resistant nozzle mount. This nozzle mount, within which the nozzle tip is mounted, is commonly referred to as a nozzle adapter.
In the past, it has been common practice to mount the nozzle tip within the nozzle adapter by brazing the tip to the adapter. The adapter was then secured to a nozzle assembly of a spray gun by a conventional threaded connection, which secured the nozzle tip in a fixed position relative to the nozzle assembly.
When used in high pressure airless spray systems, there has been a sporadic but recurring problem as a consequence of brazing failures between the nozzle and nozzle adapter. Upon failure of the brazed joint, the nozzle tip of an airless spray nozzle may be blown from the nozzle adapter toward the workpiece at a relatively high velocity with the result that it may ricochet off the workpiece or spray booth and cause a hazard to nearby personnel. A nozzle adapter having lips for mechanically locking the tip in the adapter, as discussed in U.S. Pat. No. 4,349,947, assigned to Nordson Corp., the assignee of the present invention, which patent is incorporated in its entirety herein, is one means of overcoming this problem. However, the machining and assembly requirements make this design relative expensive to manufacture.